It is proposed to study the self-associations present between certain components of the classical pathway of the complement system and also study the self-associations between subunits of mammalian pyruvate kinases. In the complement system, those interactions found between proteins in the C5,6,7,8,9 complex (membrane attack component) are particularly numerous. No one has looked at any of these associations in anything more than a qualitative manner. We will be using the direct optical gel chromatograph and analytical ultracentrifugation to quantitate these interactions. These same techniques will be used to study the subunit-subunit and metabolite-subunit interactions present in the three isozymic types of mammalian pyruvate kinase. These physical results will be correlated with the enzymatic or hemolytic activities of each system as appropriate.